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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Tantalum Capacitors
So I'm working on repairing a Korg MS2000B synthesizer for a friend with
a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case. I have little experience with tantalum capacitors. Any suggestions for a more reliable replacement? |
#2
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Tantalum Capacitors
"bitrex" wrote in message ... So I'm working on repairing a Korg MS2000B synthesizer for a friend with a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case. I have little experience with tantalum capacitors. Any suggestions for a more reliable replacement? Use 2.5 times the applied voltage or more. Or use an aluminum electrolytic 2 - 3 times capacitance. |
#3
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Tantalum Capacitors
On Tue, 22 Sep 2015 15:34:51 -0400, bitrex
wrote: So I'm working on repairing a Korg MS2000B synthesizer for a friend with a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case. I have little experience with tantalum capacitors. Any suggestions for a more reliable replacement? I don't think there's a reliability issue here. C109 (located on the Power / MIDI board schematic, is the initial output filter capacitor in a 3.3V switching power supply. There are other 100 uf caps surrounding it, but it seems to be the only tantalum cap, which suggests that the designer needed some specific characteristic of the cap to make things work. Methinks a change of capacitor type might not be such a great idea. What would make the cap explode? My guess(tm) is that someone plugged in a wrong voltage power supply, which blew up FET (F1) which then applied overvoltage to the tantalum. It much have been quite a large jolt as tantalums using produce a low resistance "short" which then gets hot and starts smoking toxic fumes. I would look around for other parts in the power supply section that may be been destroyed, such as the other caps along the 3.3V rail. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#4
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Tantalum Capacitors
On 9/22/2015 3:56 PM, Jeff Liebermann wrote:
On Tue, 22 Sep 2015 15:34:51 -0400, bitrex wrote: So I'm working on repairing a Korg MS2000B synthesizer for a friend with a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case. I have little experience with tantalum capacitors. Any suggestions for a more reliable replacement? I don't think there's a reliability issue here. C109 (located on the Power / MIDI board schematic, is the initial output filter capacitor in a 3.3V switching power supply. There are other 100 uf caps surrounding it, but it seems to be the only tantalum cap, which suggests that the designer needed some specific characteristic of the cap to make things work. Methinks a change of capacitor type might not be such a great idea. What would make the cap explode? My guess(tm) is that someone plugged in a wrong voltage power supply, which blew up FET (F1) which then applied overvoltage to the tantalum. It much have been quite a large jolt as tantalums using produce a low resistance "short" which then gets hot and starts smoking toxic fumes. I would look around for other parts in the power supply section that may be been destroyed, such as the other caps along the 3.3V rail. I notice now that there seems to be some very light heat discoloration around the common mode choke L10-L11-L12. I don't see anything immediately wrong with F1 and it passes the "smell test" so I dunno. |
#5
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Tantalum Capacitors
On Tue, 22 Sep 2015 12:56:56 -0700, Jeff Liebermann
wrote: On Tue, 22 Sep 2015 15:34:51 -0400, bitrex wrote: So I'm working on repairing a Korg MS2000B synthesizer for a friend with a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case. I have little experience with tantalum capacitors. Any suggestions for a more reliable replacement? I don't think there's a reliability issue here. C109 (located on the Power / MIDI board schematic, is the initial output filter capacitor in a 3.3V switching power supply. There are other 100 uf caps surrounding it, but it seems to be the only tantalum cap, which suggests that the designer needed some specific characteristic of the cap to make things work. Methinks a change of capacitor type might not be such a great idea. What would make the cap explode? My guess(tm) is that someone plugged in a wrong voltage power supply, which blew up FET (F1) which then applied overvoltage to the tantalum. It much have been quite a large jolt as tantalums using produce a low resistance "short" which then gets hot and starts smoking toxic fumes. I would look around for other parts in the power supply section that may be been destroyed, such as the other caps along the 3.3V rail. Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. Derate them 3:1 on voltage, or use something else. Polymer aluminums are good, and some come in a tantalum-like surface mount package. |
#6
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Tantalum Capacitors
On 22/09/2015 21:40, John Larkin wrote:
On Tue, 22 Sep 2015 12:56:56 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 15:34:51 -0400, bitrex wrote: So I'm working on repairing a Korg MS2000B synthesizer for a friend with a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case. I have little experience with tantalum capacitors. Any suggestions for a more reliable replacement? I don't think there's a reliability issue here. C109 (located on the Power / MIDI board schematic, is the initial output filter capacitor in a 3.3V switching power supply. There are other 100 uf caps surrounding it, but it seems to be the only tantalum cap, which suggests that the designer needed some specific characteristic of the cap to make things work. Methinks a change of capacitor type might not be such a great idea. What would make the cap explode? My guess(tm) is that someone plugged in a wrong voltage power supply, which blew up FET (F1) which then applied overvoltage to the tantalum. It much have been quite a large jolt as tantalums using produce a low resistance "short" which then gets hot and starts smoking toxic fumes. I would look around for other parts in the power supply section that may be been destroyed, such as the other caps along the 3.3V rail. Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. Derate them 3:1 on voltage, or use something else. Polymer aluminums are good, and some come in a tantalum-like surface mount package. +1 Cheers -- Syd |
#7
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Tantalum Capacitors
On 9/22/2015 4:40 PM, John Larkin wrote:
On Tue, 22 Sep 2015 12:56:56 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 15:34:51 -0400, bitrex wrote: So I'm working on repairing a Korg MS2000B synthesizer for a friend with a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case. I have little experience with tantalum capacitors. Any suggestions for a more reliable replacement? I don't think there's a reliability issue here. C109 (located on the Power / MIDI board schematic, is the initial output filter capacitor in a 3.3V switching power supply. There are other 100 uf caps surrounding it, but it seems to be the only tantalum cap, which suggests that the designer needed some specific characteristic of the cap to make things work. Methinks a change of capacitor type might not be such a great idea. What would make the cap explode? My guess(tm) is that someone plugged in a wrong voltage power supply, which blew up FET (F1) which then applied overvoltage to the tantalum. It much have been quite a large jolt as tantalums using produce a low resistance "short" which then gets hot and starts smoking toxic fumes. I would look around for other parts in the power supply section that may be been destroyed, such as the other caps along the 3.3V rail. Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. Derate them 3:1 on voltage, or use something else. Polymer aluminums are good, and some come in a tantalum-like surface mount package. Is there anything I can use temporarily in its place, that I might have in stock, to try and get that switcher up and running while I wait for the appropriate part? |
#8
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Tantalum Capacitors
On Tue, 22 Sep 2015 20:22:49 -0400, bitrex
wrote: On 9/22/2015 4:40 PM, John Larkin wrote: On Tue, 22 Sep 2015 12:56:56 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 15:34:51 -0400, bitrex wrote: So I'm working on repairing a Korg MS2000B synthesizer for a friend with a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf What a horrible schematic! A mosfet is "F1" and a fuse is "FU1" ! Connector names are all over the place. And worse. Replace C109 with most any 100 uF cap. What's with the 21 resistors between AGND and DGND? That's crazy. |
#9
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Tantalum Capacitors
On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin
wrote: Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. That's what I've read everywhere. Yet, I spent 10 years shipping marine radios that were literally crammed with dipped and molded tantalum caps on power supply rails with never a problem. The only ones I've ever seen go up in smoke were reverse polarized (which produced an impressive red glowing piece of slag and plenty of white smog). Mostly, these caps were 25V caps on the 12V (nominal) power supply lines and 16V caps on the 8 and 10V regulated lines. There were also a bunch used in audio circuits. However, we never used tantalums on the output of a switcher, where I would expect problems. I guess using a tantalum in this 3.3V switcher would qualify. However, at the time (1970's) the literature declared that high voltage spikes were the culprit, not voltage slew rate. Since these often appear together, I can see where there might be some confusion. Derate them 3:1 on voltage, or use something else. Polymer aluminums are good, and some come in a tantalum-like surface mount package. The original cap is a 100uF 10v tantalum which is already 3:1 derated in a 3.3 VDC power supply. However, that doesn't included voltage spikes from the nearby inductor. Judging by the age of the Korg, I would guess(tm) axial leads not SMT. 100uf 10-16V From Digikey: http://www.digikey.com/product-search/en?pv13=67&pv63=19&pv63=11&pv63=449&pv63=489&pv69= 80&FV=fff40002%2Cfff80532&mnonly=0&newproducts=0&C olumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize =25 For fast delivery, there's probably something on eBay: http://www.ebay.com/sch/i.html?_nkw=polymer+capacitor+100uf -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#10
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Tantalum Capacitors
On 9/22/2015 8:55 PM, Jeff Liebermann wrote:
On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin wrote: Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. That's what I've read everywhere. Yet, I spent 10 years shipping marine radios that were literally crammed with dipped and molded tantalum caps on power supply rails with never a problem. The only ones I've ever seen go up in smoke were reverse polarized (which produced an impressive red glowing piece of slag and plenty of white smog). Mostly, these caps were 25V caps on the 12V (nominal) power supply lines and 16V caps on the 8 and 10V regulated lines. There were also a bunch used in audio circuits. However, we never used tantalums on the output of a switcher, where I would expect problems. I guess using a tantalum in this 3.3V switcher would qualify. However, at the time (1970's) the literature declared that high voltage spikes were the culprit, not voltage slew rate. Since these often appear together, I can see where there might be some confusion. Derate them 3:1 on voltage, or use something else. Polymer aluminums are good, and some come in a tantalum-like surface mount package. The original cap is a 100uF 10v tantalum which is already 3:1 derated in a 3.3 VDC power supply. However, that doesn't included voltage spikes from the nearby inductor. Judging by the age of the Korg, I would guess(tm) axial leads not SMT. 100uf 10-16V From Digikey: http://www.digikey.com/product-search/en?pv13=67&pv63=19&pv63=11&pv63=449&pv63=489&pv69= 80&FV=fff40002%2Cfff80532&mnonly=0&newproducts=0&C olumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize =25 For fast delivery, there's probably something on eBay: http://www.ebay.com/sch/i.html?_nkw=polymer+capacitor+100uf Nope, the power supply is almost all SMT, including the tantalum. The only through hole parts is the switcher inductor and the other large capacitors, which are a mix of organic polymer and regular electrolytic. |
#11
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Tantalum Capacitors
On 9/22/2015 8:55 PM, Jeff Liebermann wrote:
On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin wrote: Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. That's what I've read everywhere. Yet, I spent 10 years shipping marine radios that were literally crammed with dipped and molded tantalum caps on power supply rails with never a problem. The only ones I've ever seen go up in smoke were reverse polarized (which produced an impressive red glowing piece of slag and plenty of white smog). Mostly, these caps were 25V caps on the 12V (nominal) power supply lines and 16V caps on the 8 and 10V regulated lines. There were also a bunch used in audio circuits. However, we never used tantalums on the output of a switcher, where I would expect problems. I guess using a tantalum in this 3.3V switcher would qualify. However, at the time (1970's) the literature declared that high voltage spikes were the culprit, not voltage slew rate. Since these often appear together, I can see where there might be some confusion. Derate them 3:1 on voltage, or use something else. Polymer aluminums are good, and some come in a tantalum-like surface mount package. The original cap is a 100uF 10v tantalum which is already 3:1 derated in a 3.3 VDC power supply. However, that doesn't included voltage spikes from the nearby inductor. Judging by the age of the Korg, I would guess(tm) axial leads not SMT. 100uf 10-16V From Digikey: http://www.digikey.com/product-search/en?pv13=67&pv63=19&pv63=11&pv63=449&pv63=489&pv69= 80&FV=fff40002%2Cfff80532&mnonly=0&newproducts=0&C olumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize =25 For fast delivery, there's probably something on eBay: http://www.ebay.com/sch/i.html?_nkw=polymer+capacitor+100uf This thing cost an arm and a leg when it was new 15 years ago. Inside the very large case there actually isn't very much - there's a board which holds all the front panel controls, and everything else including the power supply and output jacks are on a single mainboard measuring maybe 8"x10". |
#12
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Tantalum Capacitors
On Tue, 22 Sep 2015 21:23:47 -0400, bitrex
wrote: Judging by the age of the Korg, I would guess(tm) axial leads not SMT. 100uf 10-16V From Digikey: http://www.digikey.com/product-search/en?pv13=67&pv63=19&pv63=11&pv63=449&pv63=489&pv69= 80&FV=fff40002%2Cfff80532&mnonly=0&newproducts=0&C olumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize =25 For fast delivery, there's probably something on eBay: http://www.ebay.com/sch/i.html?_nkw=polymer+capacitor+100uf Nope, the power supply is almost all SMT, including the tantalum. The only through hole parts is the switcher inductor and the other large capacitors, which are a mix of organic polymer and regular electrolytic. Bad guess(tm). Sorry. I couldn't tell from the "manual" because none of the caps are listed in the parts list. This should work for SMT on Digikey: http://www.digikey.com/product-search/en?pv13=67&pv63=19&pv63=11&pv63=449&pv63=489&pv69= 3&FV=fff40002%2Cfff80532&mnonly=0&newproducts=0&Co lumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize= 25 The eBay link includes both through-hole and SMT. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#13
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Tantalum Capacitors
On Tue, 22 Sep 2015 17:55:51 -0700, Jeff Liebermann
wrote: On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin wrote: Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. That's what I've read everywhere. Yet, I spent 10 years shipping marine radios that were literally crammed with dipped and molded tantalum caps on power supply rails with never a problem. The only ones I've ever seen go up in smoke were reverse polarized (which produced an impressive red glowing piece of slag and plenty of white smog). Mostly, these caps were 25V caps on the 12V (nominal) power supply lines and 16V caps on the 8 and 10V regulated lines. There were also a bunch used in audio circuits. The tantalum thing is very erratic. Some batches blow up, some are fine. However, we never used tantalums on the output of a switcher, where I would expect problems. I guess using a tantalum in this 3.3V switcher would qualify. However, at the time (1970's) the literature declared that high voltage spikes were the culprit, not voltage slew rate. Since these often appear together, I can see where there might be some confusion. I know for sure that tantalums sometimes blow up at below their rated voltages, with no overshoot spikes. It's dV/dT, namely peak current, that can ignite tiny particles of tantalum, which then burn in the solid MnO2 electrolyte. Derate them 3:1 on voltage, or use something else. Polymer aluminums are good, and some come in a tantalum-like surface mount package. The original cap is a 100uF 10v tantalum which is already 3:1 derated in a 3.3 VDC power supply. However, that doesn't included voltage spikes from the nearby inductor. Could be. Or maybe there was a lot of dV/dT. Or maybe some other failure mechanism. Tantalums are just right for some things, but have to be used carefully. https://dl.dropboxusercontent.com/u/.../Caps/Bang.jpg https://dl.dropboxusercontent.com/u/...ied_Tant_1.JPG |
#14
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Tantalum Capacitors
On Tue, 22 Sep 2015 17:55:51 -0700, Jeff Liebermann wrote:
On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin wrote: Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. That's what I've read everywhere. Yet, I spent 10 years shipping marine radios that were literally crammed with dipped and molded tantalum caps on power supply rails with never a problem. The only ones I've ever seen go up in smoke were reverse polarized (which produced an impressive red glowing piece of slag and plenty of white smog). Mostly, these caps were 25V caps on the 12V (nominal) power supply lines and 16V caps on the 8 and 10V regulated lines. There were also a bunch used in audio circuits. However, we never used tantalums on the output of a switcher, where I would expect problems. I guess using a tantalum in this 3.3V switcher would qualify. However, at the time (1970's) the literature declared that high voltage spikes were the culprit, not voltage slew rate. Since these often appear together, I can see where there might be some confusion. Tantalums have such a low HF resistance that it is sometimes recommended to put a current limiting resistor in series if there is a serious ripple voltage around. I've witnessed a lot of IGBT's being blown up because those resistors were failing. The voltage feeding the tantalums had such a large HF ripple due to the switching of the IGBT's that it blew the tantalums out of the control board, after which the IGBT's also went to pieces. joe Derate them 3:1 on voltage, or use something else. Polymer aluminums are good, and some come in a tantalum-like surface mount package. The original cap is a 100uF 10v tantalum which is already 3:1 derated in a 3.3 VDC power supply. However, that doesn't included voltage spikes from the nearby inductor. Judging by the age of the Korg, I would guess(tm) axial leads not SMT. 100uf 10-16V From Digikey: http://www.digikey.com/product-search/en? pv13=67&pv63=19&pv63=11&pv63=449&pv63=489&pv69=80& FV=fff40002% 2Cfff80532&mnonly=0&newproducts=0&ColumnSort=0&pag e=1&quantity=0&ptm=0&fid=0&pageSize=25 For fast delivery, there's probably something on eBay: http://www.ebay.com/sch/i.html?_nkw=polymer+capacitor+100uf |
#15
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Tantalum Capacitors
On Tue, 22 Sep 2015 19:02:33 -0700, John Larkin wrote:
On Tue, 22 Sep 2015 17:55:51 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin wrote: Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. That's what I've read everywhere. Yet, I spent 10 years shipping marine radios that were literally crammed with dipped and molded tantalum caps on power supply rails with never a problem. The only ones I've ever seen go up in smoke were reverse polarized (which produced an impressive red glowing piece of slag and plenty of white smog). Mostly, these caps were 25V caps on the 12V (nominal) power supply lines and 16V caps on the 8 and 10V regulated lines. There were also a bunch used in audio circuits. The tantalum thing is very erratic. Some batches blow up, some are fine. However, we never used tantalums on the output of a switcher, where I would expect problems. I guess using a tantalum in this 3.3V switcher would qualify. However, at the time (1970's) the literature declared that high voltage spikes were the culprit, not voltage slew rate. Since these often appear together, I can see where there might be some confusion. I know for sure that tantalums sometimes blow up at below their rated voltages, with no overshoot spikes. It's dV/dT, namely peak current, that can ignite tiny particles of tantalum, which then burn in the solid MnO2 electrolyte. That's why in those cases a series resistor might be recommended in order to limit the current spikes. joe Derate them 3:1 on voltage, or use something else. Polymer aluminums are good, and some come in a tantalum-like surface mount package. The original cap is a 100uF 10v tantalum which is already 3:1 derated in a 3.3 VDC power supply. However, that doesn't included voltage spikes from the nearby inductor. Could be. Or maybe there was a lot of dV/dT. Or maybe some other failure mechanism. Tantalums are just right for some things, but have to be used carefully. https://dl.dropboxusercontent.com/u/.../Caps/Bang.jpg https://dl.dropboxusercontent.com/u/...ied_Tant_1.JPG |
#16
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Tantalum Capacitors
In sci.electronics.repair John Larkin wrote:
On Tue, 22 Sep 2015 15:34:51 -0400, bitrex wrote: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf What's with the 21 resistors between AGND and DGND? That's crazy. They're all marked "NU", which seems to mean Not Used. Other parts of that sheet have "NU" resistors in similar nonsensical places, like across the fuse or across the power switch. I suspect there are places for all of these resistors on the board, but they don't populate them at the factory except for test. Matt Roberds |
#17
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Tantalum Capacitors
On 9/23/2015 12:20 AM, joe hey wrote:
On Tue, 22 Sep 2015 19:02:33 -0700, John Larkin wrote: On Tue, 22 Sep 2015 17:55:51 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin wrote: Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. That's what I've read everywhere. Yet, I spent 10 years shipping marine radios that were literally crammed with dipped and molded tantalum caps on power supply rails with never a problem. The only ones I've ever seen go up in smoke were reverse polarized (which produced an impressive red glowing piece of slag and plenty of white smog). Mostly, these caps were 25V caps on the 12V (nominal) power supply lines and 16V caps on the 8 and 10V regulated lines. There were also a bunch used in audio circuits. The tantalum thing is very erratic. Some batches blow up, some are fine. However, we never used tantalums on the output of a switcher, where I would expect problems. I guess using a tantalum in this 3.3V switcher would qualify. However, at the time (1970's) the literature declared that high voltage spikes were the culprit, not voltage slew rate. Since these often appear together, I can see where there might be some confusion. I know for sure that tantalums sometimes blow up at below their rated voltages, with no overshoot spikes. It's dV/dT, namely peak current, that can ignite tiny particles of tantalum, which then burn in the solid MnO2 electrolyte. That's why in those cases a series resistor might be recommended in order to limit the current spikes. Add series resistance to a tantalum cap and you have just created an electrolytic replacement. -- Rick |
#18
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Tantalum Capacitors
On 23/09/2015 5:34 AM, bitrex wrote:
So I'm working on repairing a Korg MS2000B synthesizer for a friend with a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case. I have little experience with tantalum capacitors. Any suggestions for a more reliable replacement? **Tants are not unreliable. In fact, IME, they're more reliable than aluminium electros (not a scientific study though - just seat of the pants). They do not tolerate reverse Voltages particularly well though. Use another tantalum. Solid are best, but hard to find. -- Trevor Wilson www.rageaudio.com.au --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
#19
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Tantalum Capacitors
On Wed, 23 Sep 2015 00:40:00 -0400, rickman wrote:
On 9/23/2015 12:20 AM, joe hey wrote: On Tue, 22 Sep 2015 19:02:33 -0700, John Larkin wrote: On Tue, 22 Sep 2015 17:55:51 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin wrote: Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. That's what I've read everywhere. Yet, I spent 10 years shipping marine radios that were literally crammed with dipped and molded tantalum caps on power supply rails with never a problem. The only ones I've ever seen go up in smoke were reverse polarized (which produced an impressive red glowing piece of slag and plenty of white smog). Mostly, these caps were 25V caps on the 12V (nominal) power supply lines and 16V caps on the 8 and 10V regulated lines. There were also a bunch used in audio circuits. The tantalum thing is very erratic. Some batches blow up, some are fine. However, we never used tantalums on the output of a switcher, where I would expect problems. I guess using a tantalum in this 3.3V switcher would qualify. However, at the time (1970's) the literature declared that high voltage spikes were the culprit, not voltage slew rate. Since these often appear together, I can see where there might be some confusion. I know for sure that tantalums sometimes blow up at below their rated voltages, with no overshoot spikes. It's dV/dT, namely peak current, that can ignite tiny particles of tantalum, which then burn in the solid MnO2 electrolyte. That's why in those cases a series resistor might be recommended in order to limit the current spikes. Add series resistance to a tantalum cap and you have just created an electrolytic replacement. Sorry, I forgot to mention to put the resistance in between the power line and the tantalum. joe |
#20
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Tantalum Capacitors
On 09/22/2015 06:18 PM, Syd Rumpo wrote:
On 22/09/2015 21:40, John Larkin wrote: On Tue, 22 Sep 2015 12:56:56 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 15:34:51 -0400, bitrex wrote: So I'm working on repairing a Korg MS2000B synthesizer for a friend with a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case. I have little experience with tantalum capacitors. Any suggestions for a more reliable replacement? I don't think there's a reliability issue here. C109 (located on the Power / MIDI board schematic, is the initial output filter capacitor in a 3.3V switching power supply. There are other 100 uf caps surrounding it, but it seems to be the only tantalum cap, which suggests that the designer needed some specific characteristic of the cap to make things work. Methinks a change of capacitor type might not be such a great idea. What would make the cap explode? My guess(tm) is that someone plugged in a wrong voltage power supply, which blew up FET (F1) which then applied overvoltage to the tantalum. It much have been quite a large jolt as tantalums using produce a low resistance "short" which then gets hot and starts smoking toxic fumes. I would look around for other parts in the power supply section that may be been destroyed, such as the other caps along the 3.3V rail. Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. Derate them 3:1 on voltage, or use something else. Polymer aluminums are good, and some come in a tantalum-like surface mount package. +1 Cheers Al polys can make voltage regulators oscillate. Tantalums have a nice middle-of-the-road ESR that makes 7800s happy. The ignition problem is quite real--see http://electrooptical.net/www/sed/TantalumCapReforming_25272-what_a_cap_astrophe.pdf Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net |
#21
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Tantalum Capacitors
On Wed, 23 Sep 2015 09:31:20 -0400, Phil Hobbs
wrote: On 09/22/2015 06:18 PM, Syd Rumpo wrote: On 22/09/2015 21:40, John Larkin wrote: On Tue, 22 Sep 2015 12:56:56 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 15:34:51 -0400, bitrex wrote: So I'm working on repairing a Korg MS2000B synthesizer for a friend with a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case. I have little experience with tantalum capacitors. Any suggestions for a more reliable replacement? I don't think there's a reliability issue here. C109 (located on the Power / MIDI board schematic, is the initial output filter capacitor in a 3.3V switching power supply. There are other 100 uf caps surrounding it, but it seems to be the only tantalum cap, which suggests that the designer needed some specific characteristic of the cap to make things work. Methinks a change of capacitor type might not be such a great idea. What would make the cap explode? My guess(tm) is that someone plugged in a wrong voltage power supply, which blew up FET (F1) which then applied overvoltage to the tantalum. It much have been quite a large jolt as tantalums using produce a low resistance "short" which then gets hot and starts smoking toxic fumes. I would look around for other parts in the power supply section that may be been destroyed, such as the other caps along the 3.3V rail. Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. Derate them 3:1 on voltage, or use something else. Polymer aluminums are good, and some come in a tantalum-like surface mount package. +1 Cheers Al polys can make voltage regulators oscillate. Tantalums have a nice middle-of-the-road ESR that makes 7800s happy. My favorite cheap "MDO" regulator, the LM1117, loves a 10 uF tantalum on its output. |
#22
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Tantalum Capacitors
On 23 Sep 2015 11:06:49 GMT, joe hey wrote:
On Wed, 23 Sep 2015 00:40:00 -0400, rickman wrote: On 9/23/2015 12:20 AM, joe hey wrote: On Tue, 22 Sep 2015 19:02:33 -0700, John Larkin wrote: On Tue, 22 Sep 2015 17:55:51 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin wrote: Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. That's what I've read everywhere. Yet, I spent 10 years shipping marine radios that were literally crammed with dipped and molded tantalum caps on power supply rails with never a problem. The only ones I've ever seen go up in smoke were reverse polarized (which produced an impressive red glowing piece of slag and plenty of white smog). Mostly, these caps were 25V caps on the 12V (nominal) power supply lines and 16V caps on the 8 and 10V regulated lines. There were also a bunch used in audio circuits. The tantalum thing is very erratic. Some batches blow up, some are fine. However, we never used tantalums on the output of a switcher, where I would expect problems. I guess using a tantalum in this 3.3V switcher would qualify. However, at the time (1970's) the literature declared that high voltage spikes were the culprit, not voltage slew rate. Since these often appear together, I can see where there might be some confusion. I know for sure that tantalums sometimes blow up at below their rated voltages, with no overshoot spikes. It's dV/dT, namely peak current, that can ignite tiny particles of tantalum, which then burn in the solid MnO2 electrolyte. That's why in those cases a series resistor might be recommended in order to limit the current spikes. Add series resistance to a tantalum cap and you have just created an electrolytic replacement. Sorry, I forgot to mention to put the resistance in between the power line and the tantalum. But than it doesn't bypass the power rail! |
#23
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Tantalum Capacitors
On Wed, 23 Sep 2015 16:01:26 +1000, Trevor Wilson
wrote: On 23/09/2015 5:34 AM, bitrex wrote: So I'm working on repairing a Korg MS2000B synthesizer for a friend with a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case. I have little experience with tantalum capacitors. Any suggestions for a more reliable replacement? **Tants are not unreliable. In fact, IME, they're more reliable than aluminium electros (not a scientific study though - just seat of the pants). They do not tolerate reverse Voltages particularly well though. Use another tantalum. Solid are best, but hard to find. Most tantalum caps are solids, with the MnO2 electrolyte. Less common are liquid types and polymers. |
#24
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Tantalum Capacitors
wrote in message ... In sci.electronics.repair John Larkin wrote: On Tue, 22 Sep 2015 15:34:51 -0400, bitrex wrote: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf What's with the 21 resistors between AGND and DGND? That's crazy. They're all marked "NU", which seems to mean Not Used. Other parts of that sheet have "NU" resistors in similar nonsensical places, like across the fuse or across the power switch. I suspect there are places for all of these resistors on the board, but they don't populate them at the factory except for test. That is somewhat of a crazy schematic. I bet some of the NU resistors could be some 0 ohm resistors. They are mainly jumper wires made inside a blob of material that resembles a resistor in size. They have been used to be in inserted by machine to jump over places where a circuit trace can not be made. |
#25
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Tantalum Capacitors
On Wed, 23 Sep 2015 07:22:29 -0700, John Larkin wrote:
On 23 Sep 2015 11:06:49 GMT, joe hey wrote: On Wed, 23 Sep 2015 00:40:00 -0400, rickman wrote: On 9/23/2015 12:20 AM, joe hey wrote: On Tue, 22 Sep 2015 19:02:33 -0700, John Larkin wrote: On Tue, 22 Sep 2015 17:55:51 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin wrote: Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. That's what I've read everywhere. Yet, I spent 10 years shipping marine radios that were literally crammed with dipped and molded tantalum caps on power supply rails with never a problem. The only ones I've ever seen go up in smoke were reverse polarized (which produced an impressive red glowing piece of slag and plenty of white smog). Mostly, these caps were 25V caps on the 12V (nominal) power supply lines and 16V caps on the 8 and 10V regulated lines. There were also a bunch used in audio circuits. The tantalum thing is very erratic. Some batches blow up, some are fine. However, we never used tantalums on the output of a switcher, where I would expect problems. I guess using a tantalum in this 3.3V switcher would qualify. However, at the time (1970's) the literature declared that high voltage spikes were the culprit, not voltage slew rate. Since these often appear together, I can see where there might be some confusion. I know for sure that tantalums sometimes blow up at below their rated voltages, with no overshoot spikes. It's dV/dT, namely peak current, that can ignite tiny particles of tantalum, which then burn in the solid MnO2 electrolyte. That's why in those cases a series resistor might be recommended in order to limit the current spikes. Add series resistance to a tantalum cap and you have just created an electrolytic replacement. Sorry, I forgot to mention to put the resistance in between the power line and the tantalum. But than it doesn't bypass the power rail! No, we did it locally, every IC that was uncoupled with a tantalum, we put a small resistor from the power rail to the tantalum and the problem was solved. I clearly remember reading this advice in some tantalum's datasheet or application note. As those IC's consume very little, the DC voltage drop over the resistance was negligible, but the reduction in current spikes through the tantalums was considerable. They didn't blow up anymore and neither did the IGBTs. joe |
#26
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Tantalum Capacitors
In sci.electronics.repair Phil Hobbs wrote:
On 09/22/2015 06:18 PM, Syd Rumpo wrote: On 22/09/2015 21:40, John Larkin wrote: On Tue, 22 Sep 2015 12:56:56 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 15:34:51 -0400, bitrex wrote: So I'm working on repairing a Korg MS2000B synthesizer for a friend with a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case. I have little experience with tantalum capacitors. Any suggestions for a more reliable replacement? I don't think there's a reliability issue here. C109 (located on the Power / MIDI board schematic, is the initial output filter capacitor in a 3.3V switching power supply. There are other 100 uf caps surrounding it, but it seems to be the only tantalum cap, which suggests that the designer needed some specific characteristic of the cap to make things work. Methinks a change of capacitor type might not be such a great idea. What would make the cap explode? My guess(tm) is that someone plugged in a wrong voltage power supply, which blew up FET (F1) which then applied overvoltage to the tantalum. It much have been quite a large jolt as tantalums using produce a low resistance "short" which then gets hot and starts smoking toxic fumes. I would look around for other parts in the power supply section that may be been destroyed, such as the other caps along the 3.3V rail. Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. Derate them 3:1 on voltage, or use something else. Polymer aluminums are good, and some come in a tantalum-like surface mount package. +1 Cheers Al polys can make voltage regulators oscillate. Tantalums have a nice middle-of-the-road ESR that makes 7800s happy. The ignition problem is quite real--see http://electrooptical.net/www/sed/TantalumCapReforming_25272-what_a_cap_astrophe.pdf Can somebody decode "postprocessing fixture" back into English? I have idea what the author is talking about or what the "fix" really was. |
#27
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Tantalum Capacitors
On 09/23/2015 12:08 PM, Cydrome Leader wrote:
In sci.electronics.repair Phil Hobbs wrote: On 09/22/2015 06:18 PM, Syd Rumpo wrote: On 22/09/2015 21:40, John Larkin wrote: On Tue, 22 Sep 2015 12:56:56 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 15:34:51 -0400, bitrex wrote: So I'm working on repairing a Korg MS2000B synthesizer for a friend with a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case. I have little experience with tantalum capacitors. Any suggestions for a more reliable replacement? I don't think there's a reliability issue here. C109 (located on the Power / MIDI board schematic, is the initial output filter capacitor in a 3.3V switching power supply. There are other 100 uf caps surrounding it, but it seems to be the only tantalum cap, which suggests that the designer needed some specific characteristic of the cap to make things work. Methinks a change of capacitor type might not be such a great idea. What would make the cap explode? My guess(tm) is that someone plugged in a wrong voltage power supply, which blew up FET (F1) which then applied overvoltage to the tantalum. It much have been quite a large jolt as tantalums using produce a low resistance "short" which then gets hot and starts smoking toxic fumes. I would look around for other parts in the power supply section that may be been destroyed, such as the other caps along the 3.3V rail. Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. Derate them 3:1 on voltage, or use something else. Polymer aluminums are good, and some come in a tantalum-like surface mount package. +1 Cheers Al polys can make voltage regulators oscillate. Tantalums have a nice middle-of-the-road ESR that makes 7800s happy. The ignition problem is quite real--see http://electrooptical.net/www/sed/TantalumCapReforming_25272-what_a_cap_astrophe.pdf Can somebody decode "postprocessing fixture" back into English? I have idea what the author is talking about or what the "fix" really was. He ramped up the supply slowly with a current limit, to give the tants a chance to clear the damage. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net |
#28
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Tantalum Capacitors
On 9/23/2015 12:26 PM, Phil Hobbs wrote:
On 09/23/2015 12:08 PM, Cydrome Leader wrote: In sci.electronics.repair Phil Hobbs wrote: On 09/22/2015 06:18 PM, Syd Rumpo wrote: On 22/09/2015 21:40, John Larkin wrote: On Tue, 22 Sep 2015 12:56:56 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 15:34:51 -0400, bitrex wrote: So I'm working on repairing a Korg MS2000B synthesizer for a friend with a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case. I have little experience with tantalum capacitors. Any suggestions for a more reliable replacement? I don't think there's a reliability issue here. C109 (located on the Power / MIDI board schematic, is the initial output filter capacitor in a 3.3V switching power supply. There are other 100 uf caps surrounding it, but it seems to be the only tantalum cap, which suggests that the designer needed some specific characteristic of the cap to make things work. Methinks a change of capacitor type might not be such a great idea. What would make the cap explode? My guess(tm) is that someone plugged in a wrong voltage power supply, which blew up FET (F1) which then applied overvoltage to the tantalum. It much have been quite a large jolt as tantalums using produce a low resistance "short" which then gets hot and starts smoking toxic fumes. I would look around for other parts in the power supply section that may be been destroyed, such as the other caps along the 3.3V rail. Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. Derate them 3:1 on voltage, or use something else. Polymer aluminums are good, and some come in a tantalum-like surface mount package. +1 Cheers Al polys can make voltage regulators oscillate. Tantalums have a nice middle-of-the-road ESR that makes 7800s happy. The ignition problem is quite real--see http://electrooptical.net/www/sed/TantalumCapReforming_25272-what_a_cap_astrophe.pdf Can somebody decode "postprocessing fixture" back into English? I have idea what the author is talking about or what the "fix" really was. He ramped up the supply slowly with a current limit, to give the tants a chance to clear the damage. Is it about clearing damage or just to show the added resistance prevented the failure? I found the story a bit hard to follow. -- Rick |
#29
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Tantalum Capacitors
On 23 Sep 2015 15:24:36 GMT, joe hey wrote:
On Wed, 23 Sep 2015 07:22:29 -0700, John Larkin wrote: On 23 Sep 2015 11:06:49 GMT, joe hey wrote: On Wed, 23 Sep 2015 00:40:00 -0400, rickman wrote: On 9/23/2015 12:20 AM, joe hey wrote: On Tue, 22 Sep 2015 19:02:33 -0700, John Larkin wrote: On Tue, 22 Sep 2015 17:55:51 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin wrote: Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. That's what I've read everywhere. Yet, I spent 10 years shipping marine radios that were literally crammed with dipped and molded tantalum caps on power supply rails with never a problem. The only ones I've ever seen go up in smoke were reverse polarized (which produced an impressive red glowing piece of slag and plenty of white smog). Mostly, these caps were 25V caps on the 12V (nominal) power supply lines and 16V caps on the 8 and 10V regulated lines. There were also a bunch used in audio circuits. The tantalum thing is very erratic. Some batches blow up, some are fine. However, we never used tantalums on the output of a switcher, where I would expect problems. I guess using a tantalum in this 3.3V switcher would qualify. However, at the time (1970's) the literature declared that high voltage spikes were the culprit, not voltage slew rate. Since these often appear together, I can see where there might be some confusion. I know for sure that tantalums sometimes blow up at below their rated voltages, with no overshoot spikes. It's dV/dT, namely peak current, that can ignite tiny particles of tantalum, which then burn in the solid MnO2 electrolyte. That's why in those cases a series resistor might be recommended in order to limit the current spikes. Add series resistance to a tantalum cap and you have just created an electrolytic replacement. Sorry, I forgot to mention to put the resistance in between the power line and the tantalum. But than it doesn't bypass the power rail! No, we did it locally, every IC that was uncoupled with a tantalum, we put a small resistor from the power rail to the tantalum and the problem was solved. I clearly remember reading this advice in some tantalum's datasheet or application note. As those IC's consume very little, the DC voltage drop over the resistance was negligible, but the reduction in current spikes through the tantalums was considerable. They didn't blow up anymore and neither did the IGBTs. The point being that by adding the resistor, you've increased the "ESR" of the cap(-resistor). You might just as well use an aluminum cap in its place if ESR doesn't matter. |
#30
Posted to sci.electronics.design,sci.electronics.repair
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Tantalum Capacitors
krw writes:
On 23 Sep 2015 15:24:36 GMT, joe hey wrote: On Wed, 23 Sep 2015 07:22:29 -0700, John Larkin wrote: On 23 Sep 2015 11:06:49 GMT, joe hey wrote: On Wed, 23 Sep 2015 00:40:00 -0400, rickman wrote: On 9/23/2015 12:20 AM, joe hey wrote: On Tue, 22 Sep 2015 19:02:33 -0700, John Larkin wrote: On Tue, 22 Sep 2015 17:55:51 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin wrote: Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. That's what I've read everywhere. Yet, I spent 10 years shipping marine radios that were literally crammed with dipped and molded tantalum caps on power supply rails with never a problem. The only ones I've ever seen go up in smoke were reverse polarized (which produced an impressive red glowing piece of slag and plenty of white smog). Mostly, these caps were 25V caps on the 12V (nominal) power supply lines and 16V caps on the 8 and 10V regulated lines. There were also a bunch used in audio circuits. The tantalum thing is very erratic. Some batches blow up, some are fine. However, we never used tantalums on the output of a switcher, where I would expect problems. I guess using a tantalum in this 3.3V switcher would qualify. However, at the time (1970's) the literature declared that high voltage spikes were the culprit, not voltage slew rate. Since these often appear together, I can see where there might be some confusion. I know for sure that tantalums sometimes blow up at below their rated voltages, with no overshoot spikes. It's dV/dT, namely peak current, that can ignite tiny particles of tantalum, which then burn in the solid MnO2 electrolyte. That's why in those cases a series resistor might be recommended in order to limit the current spikes. Add series resistance to a tantalum cap and you have just created an electrolytic replacement. Sorry, I forgot to mention to put the resistance in between the power line and the tantalum. But than it doesn't bypass the power rail! No, we did it locally, every IC that was uncoupled with a tantalum, we put a small resistor from the power rail to the tantalum and the problem was solved. I clearly remember reading this advice in some tantalum's datasheet or application note. As those IC's consume very little, the DC voltage drop over the resistance was negligible, but the reduction in current spikes through the tantalums was considerable. They didn't blow up anymore and neither did the IGBTs. The point being that by adding the resistor, you've increased the "ESR" of the cap(-resistor). You might just as well use an aluminum cap in its place if ESR doesn't matter. No there is still a low-ESR decoupling for the IC. I do that a lot since it isolates the IC rail from spikes on the main power rail. (Not with tants though). -- John Devereux |
#31
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Tantalum Capacitors
On 9/23/2015 12:47 PM, krw wrote:
On 23 Sep 2015 15:24:36 GMT, joe hey wrote: On Wed, 23 Sep 2015 07:22:29 -0700, John Larkin wrote: On 23 Sep 2015 11:06:49 GMT, joe hey wrote: On Wed, 23 Sep 2015 00:40:00 -0400, rickman wrote: On 9/23/2015 12:20 AM, joe hey wrote: On Tue, 22 Sep 2015 19:02:33 -0700, John Larkin wrote: On Tue, 22 Sep 2015 17:55:51 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin wrote: Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. That's what I've read everywhere. Yet, I spent 10 years shipping marine radios that were literally crammed with dipped and molded tantalum caps on power supply rails with never a problem. The only ones I've ever seen go up in smoke were reverse polarized (which produced an impressive red glowing piece of slag and plenty of white smog). Mostly, these caps were 25V caps on the 12V (nominal) power supply lines and 16V caps on the 8 and 10V regulated lines. There were also a bunch used in audio circuits. The tantalum thing is very erratic. Some batches blow up, some are fine. However, we never used tantalums on the output of a switcher, where I would expect problems. I guess using a tantalum in this 3.3V switcher would qualify. However, at the time (1970's) the literature declared that high voltage spikes were the culprit, not voltage slew rate. Since these often appear together, I can see where there might be some confusion. I know for sure that tantalums sometimes blow up at below their rated voltages, with no overshoot spikes. It's dV/dT, namely peak current, that can ignite tiny particles of tantalum, which then burn in the solid MnO2 electrolyte. That's why in those cases a series resistor might be recommended in order to limit the current spikes. Add series resistance to a tantalum cap and you have just created an electrolytic replacement. Sorry, I forgot to mention to put the resistance in between the power line and the tantalum. But than it doesn't bypass the power rail! No, we did it locally, every IC that was uncoupled with a tantalum, we put a small resistor from the power rail to the tantalum and the problem was solved. I clearly remember reading this advice in some tantalum's datasheet or application note. As those IC's consume very little, the DC voltage drop over the resistance was negligible, but the reduction in current spikes through the tantalums was considerable. They didn't blow up anymore and neither did the IGBTs. The point being that by adding the resistor, you've increased the "ESR" of the cap(-resistor). You might just as well use an aluminum cap in its place if ESR doesn't matter. He is talking about this... Vcc ---/\/\/\---+-------+ | | IC = | | --- --- - - Not this... Vcc ----+----/\/\/\-----+ | | IC = | | --- --- - - -- Rick |
#32
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Tantalum Capacitors
On 23 Sep 2015 04:18:36 GMT, joe hey wrote:
Tantalums have such a low HF resistance that it is sometimes recommended to put a current limiting resistor in series if there is a serious ripple voltage around. Really? http://my.execpc.com/~endlr/esr.html Click on the graph near the bottom of the page. Note that the low-ESR aluminum electrolytic is only slightly worse than the equivalent tantalum. If polymer caps were added to the graph, it would be about the same as tantalum. The reason we used tantalum (in marine radios) over electrolytics was that they were smaller, lasted longer, were sealed, more stable capacitance over temperature, more stable ESR over temperature, and were easier to handle in a wave solder and washing machine environment. While each benefit for tantalum is admittedly minor, the combination of all the aforementioned benefits made them quite a superior device. The only downside was the cost, which limited their use to areas where a very low ESR was needed. Your "current limiting resistor" sounds like something that would raise the ESR of the device by the resistor value. Much depends on the ripple current, which presumably in a switching power supply filter cap, is quite high. When playing with ESR's of less than 1 ohm, minor variables such as PCB plating thickness and trace width/length become significant. When the lowest ESR is at the series self resonant frequency of the capacitor, the selection of type, value, voltage, package, etc also become important. Much of the RF circuitry involved in a radio requires broadband bypassing. That rapidly becomes an exercise in capacitor selection based on series resonant frequencies and lowest overall ESR. It was not unusual to have 3 different bypass caps in parallel at key locations, such as the corners of PCB's to chassis ground points. Adding a series resistor to the tantalum cap would not have worked for obtaining the lowest possible ESR. I've witnessed a lot of IGBT's being blown up because those resistors were failing. The voltage feeding the tantalums had such a large HF ripple due to the switching of the IGBT's that it blew the tantalums out of the control board, after which the IGBT's also went to pieces. Did the ripple voltage on the power supply line increase with the added series resistance? -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#33
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Tantalum Capacitors
On Tue, 22 Sep 2015 19:02:33 -0700, John Larkin
wrote: The tantalum thing is very erratic. Some batches blow up, some are fine. I guess I should mention that Intech had two divisions. I worked for the marine radio division. There was also a "modular products" division that made military grade modules (A/D, D/A, amps, etc). Both divisions shared many of the same components including a wide selection of tantalum caps. Most of the modules ran on +15/-15 VDC and used 35 VDC rated tantalums. As I vaguely recall, there were no aluminum caps used in anything that had to work from -40C to +105C. If tantalums were that failure prone, they would never have survived in a mil spec environment. Some typical radio boards. This is Intech M3600 2-30 MHz 150 watt PEP synthesized SSB radio circa 1977(?): http://www.hellocq.net/forum/read.php?tid=226493 The boards are a mix of purple potted electrolytics and blue or orange colored tantalums. No failures in 10 years of similar radios. There also seems to be an aging mechanism involved. I'm the not so proud owner of several Wavetek 3000B service monitors: http://802.11junk.com/jeffl/pics/home/slides/BL-shop5.html Some of the tantalums have shorted over the years. I'm replacing them as I blunder forward. No fires, smoke, or discoloration in about 10 years of fixing these. I also have some other equipment with similar tantalum problems. I recently repaired an M3600 radio which showed no evidence of deteriorating or failed tantalums. Has something changed in the last 40 years in how tantalums are made? I know for sure that tantalums sometimes blow up at below their rated voltages, with no overshoot spikes. It's dV/dT, namely peak current, that can ignite tiny particles of tantalum, which then burn in the solid MnO2 electrolyte. I think you mean dI/dT which provides the heating necessary to ignite the tantalum. That all sounds logical, but doesn't explain why a similar amount of heating caused by normal ripple current doesn't set fire to the capacitor. I've seen some heat darkened tantalums operating normally without ignition. Like the bulging electrolytics and burning LiIon batteries, I suspect there's been some changes in production methods (like skipping important steps to save pennies). The original cap is a 100uF 10v tantalum which is already 3:1 derated in a 3.3 VDC power supply. However, that doesn't included voltage spikes from the nearby inductor. Could be. Or maybe there was a lot of dV/dT. Or maybe some other failure mechanism. Tantalums are just right for some things, but have to be used carefully. https://dl.dropboxusercontent.com/u/.../Caps/Bang.jpg https://dl.dropboxusercontent.com/u/...ied_Tant_1.JPG Nice photos. Having done post mortem failure analysis a few times, I like to look at the damage and try to guess what was the cause. It's fairly easy to inspect the remains and estimate the violence of the failure. For tantalum, there's usually something left of the wire leads or carbonized slug. It gets hot, belches flames, carbonizes, falls apart, which finally breaks the connection. However, the OP mentioned that: "The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case." That's not what I consider to be a conventional tantalum burn failure. The cap should have looked like the one in the above photos. Something caused this one to explode rather than burn, which is why I suggested that a much higher voltage wall wart was involved. I don't think the tantalum was at fault simply because it was the first thing to blow and was the most obvious physical failure. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#34
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Tantalum Capacitors
On 09/23/2015 01:35 PM, John Devereux wrote:
krw writes: On 23 Sep 2015 15:24:36 GMT, joe hey wrote: On Wed, 23 Sep 2015 07:22:29 -0700, John Larkin wrote: On 23 Sep 2015 11:06:49 GMT, joe hey wrote: On Wed, 23 Sep 2015 00:40:00 -0400, rickman wrote: On 9/23/2015 12:20 AM, joe hey wrote: On Tue, 22 Sep 2015 19:02:33 -0700, John Larkin wrote: On Tue, 22 Sep 2015 17:55:51 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin wrote: Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. That's what I've read everywhere. Yet, I spent 10 years shipping marine radios that were literally crammed with dipped and molded tantalum caps on power supply rails with never a problem. The only ones I've ever seen go up in smoke were reverse polarized (which produced an impressive red glowing piece of slag and plenty of white smog). Mostly, these caps were 25V caps on the 12V (nominal) power supply lines and 16V caps on the 8 and 10V regulated lines. There were also a bunch used in audio circuits. The tantalum thing is very erratic. Some batches blow up, some are fine. However, we never used tantalums on the output of a switcher, where I would expect problems. I guess using a tantalum in this 3.3V switcher would qualify. However, at the time (1970's) the literature declared that high voltage spikes were the culprit, not voltage slew rate. Since these often appear together, I can see where there might be some confusion. I know for sure that tantalums sometimes blow up at below their rated voltages, with no overshoot spikes. It's dV/dT, namely peak current, that can ignite tiny particles of tantalum, which then burn in the solid MnO2 electrolyte. That's why in those cases a series resistor might be recommended in order to limit the current spikes. Add series resistance to a tantalum cap and you have just created an electrolytic replacement. Sorry, I forgot to mention to put the resistance in between the power line and the tantalum. But than it doesn't bypass the power rail! No, we did it locally, every IC that was uncoupled with a tantalum, we put a small resistor from the power rail to the tantalum and the problem was solved. I clearly remember reading this advice in some tantalum's datasheet or application note. As those IC's consume very little, the DC voltage drop over the resistance was negligible, but the reduction in current spikes through the tantalums was considerable. They didn't blow up anymore and neither did the IGBTs. The point being that by adding the resistor, you've increased the "ESR" of the cap(-resistor). You might just as well use an aluminum cap in its place if ESR doesn't matter. No there is still a low-ESR decoupling for the IC. I do that a lot since it isolates the IC rail from spikes on the main power rail. (Not with tants though). An aluminum electro in parallel with a smaller ceramic makes a nice lead-lag network for the voltage regulator, if you do it right. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net |
#35
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Tantalum Capacitors
On Wed, 23 Sep 2015 15:19:56 -0400, Phil Hobbs
wrote: On 09/23/2015 01:35 PM, John Devereux wrote: krw writes: On 23 Sep 2015 15:24:36 GMT, joe hey wrote: On Wed, 23 Sep 2015 07:22:29 -0700, John Larkin wrote: On 23 Sep 2015 11:06:49 GMT, joe hey wrote: On Wed, 23 Sep 2015 00:40:00 -0400, rickman wrote: On 9/23/2015 12:20 AM, joe hey wrote: On Tue, 22 Sep 2015 19:02:33 -0700, John Larkin wrote: On Tue, 22 Sep 2015 17:55:51 -0700, Jeff Liebermann wrote: On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin wrote: Dry-slug tantalums across power rails are bad news. High dV/dT literally ignites them; MnO2 is the oxidizer and tantalum is the fuel. That's what I've read everywhere. Yet, I spent 10 years shipping marine radios that were literally crammed with dipped and molded tantalum caps on power supply rails with never a problem. The only ones I've ever seen go up in smoke were reverse polarized (which produced an impressive red glowing piece of slag and plenty of white smog). Mostly, these caps were 25V caps on the 12V (nominal) power supply lines and 16V caps on the 8 and 10V regulated lines. There were also a bunch used in audio circuits. The tantalum thing is very erratic. Some batches blow up, some are fine. However, we never used tantalums on the output of a switcher, where I would expect problems. I guess using a tantalum in this 3.3V switcher would qualify. However, at the time (1970's) the literature declared that high voltage spikes were the culprit, not voltage slew rate. Since these often appear together, I can see where there might be some confusion. I know for sure that tantalums sometimes blow up at below their rated voltages, with no overshoot spikes. It's dV/dT, namely peak current, that can ignite tiny particles of tantalum, which then burn in the solid MnO2 electrolyte. That's why in those cases a series resistor might be recommended in order to limit the current spikes. Add series resistance to a tantalum cap and you have just created an electrolytic replacement. Sorry, I forgot to mention to put the resistance in between the power line and the tantalum. But than it doesn't bypass the power rail! No, we did it locally, every IC that was uncoupled with a tantalum, we put a small resistor from the power rail to the tantalum and the problem was solved. I clearly remember reading this advice in some tantalum's datasheet or application note. As those IC's consume very little, the DC voltage drop over the resistance was negligible, but the reduction in current spikes through the tantalums was considerable. They didn't blow up anymore and neither did the IGBTs. The point being that by adding the resistor, you've increased the "ESR" of the cap(-resistor). You might just as well use an aluminum cap in its place if ESR doesn't matter. No there is still a low-ESR decoupling for the IC. I do that a lot since it isolates the IC rail from spikes on the main power rail. (Not with tants though). An aluminum electro in parallel with a smaller ceramic makes a nice lead-lag network for the voltage regulator, if you do it right. Cheers Phil Hobbs One thing that doesn't show up on the power supply schematic sheet is the zillions of chip bypass caps on other sheets. One might have tens of uF of paralleled super-low ESR ceramic caps on a big power pour. A tantalum seems to have the right ESR to damp the whole mess, even when a regulator should be unstable with just the ceramics. One test for stability is to apply a pulse load and see how the regulator reacts. I saw one big board (part of an Anritsu DRAM tester system) that had 3000 bypass caps. It's not unusual to see an FPGA appnote that recommends a hundred caps or so per chip. |
#36
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Tantalum Capacitors
On 09/23/2015 10:24 AM, John Larkin wrote:
On Wed, 23 Sep 2015 16:01:26 +1000, Trevor Wilson wrote: On 23/09/2015 5:34 AM, bitrex wrote: So I'm working on repairing a Korg MS2000B synthesizer for a friend with a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case. I have little experience with tantalum capacitors. Any suggestions for a more reliable replacement? **Tants are not unreliable. In fact, IME, they're more reliable than aluminium electros (not a scientific study though - just seat of the pants). They do not tolerate reverse Voltages particularly well though. Use another tantalum. Solid are best, but hard to find. Most tantalum caps are solids, with the MnO2 electrolyte. Less common are liquid types and polymers. Wet tants are super-expensive. ISTR they're basically military-only. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net |
#37
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Tantalum Capacitors
On Wed, 23 Sep 2015 16:15:59 -0400, Phil Hobbs
wrote: On 09/23/2015 10:24 AM, John Larkin wrote: On Wed, 23 Sep 2015 16:01:26 +1000, Trevor Wilson wrote: On 23/09/2015 5:34 AM, bitrex wrote: So I'm working on repairing a Korg MS2000B synthesizer for a friend with a dead power supply. Here's the service manual: http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf The first thing I notice when looking inside is that the small SMT 100uF 10V tantalum capacitor C109 has completely vacated - it appears to be gone, blown right off the board. There are some little fragments rattling around in the case. I have little experience with tantalum capacitors. Any suggestions for a more reliable replacement? **Tants are not unreliable. In fact, IME, they're more reliable than aluminium electros (not a scientific study though - just seat of the pants). They do not tolerate reverse Voltages particularly well though. Use another tantalum. Solid are best, but hard to find. Most tantalum caps are solids, with the MnO2 electrolyte. Less common are liquid types and polymers. Wet tants are super-expensive. ISTR they're basically military-only. Cheers Phil Hobbs Pretty much. We used to use them in mil systems. The cases were silver, back when silver wasn't too expensive. The electrolyte is acid, which eventually eats its way out. I think the cases may be tantalum now. CSR13 part numbers, something like that. A few bucks each, about the price of a low-end steak dinner then. |
#38
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Tantalum Capacitors
On 23/09/2015 15:24, John Larkin wrote:
Most tantalum caps are solids, with the MnO2 electrolyte. Less common are liquid types and polymers. There is even solid aluminum, now only made by Vishay (I think) and cost more than equivalent tantalum. The ones I use are resin dipped through hole parts and look like a big resin dipped tantalum bead. Nice caps, very low ESR and supposedly very reliable, claim "no-known wear-out mechanism". piglet |
#39
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Tantalum Capacitors
On Wed, 23 Sep 2015 21:34:38 +0100, piglet
wrote: On 23/09/2015 15:24, John Larkin wrote: Most tantalum caps are solids, with the MnO2 electrolyte. Less common are liquid types and polymers. There is even solid aluminum, now only made by Vishay (I think) and cost more than equivalent tantalum. The ones I use are resin dipped through hole parts and look like a big resin dipped tantalum bead. Nice caps, very low ESR and supposedly very reliable, claim "no-known wear-out mechanism". piglet Do you mean polymer aluminums? Those are great, super low ESR. We use United Chem-Com and Nichicon. 47 cents for 180 uF 6.3 volts, about 2x tha price of a regular aluminum cap. |
#40
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Tantalum Capacitors
On 23/09/2015 21:56, John Larkin wrote:
On Wed, 23 Sep 2015 21:34:38 +0100, piglet wrote: On 23/09/2015 15:24, John Larkin wrote: Most tantalum caps are solids, with the MnO2 electrolyte. Less common are liquid types and polymers. There is even solid aluminum, now only made by Vishay (I think) and cost more than equivalent tantalum. The ones I use are resin dipped through hole parts and look like a big resin dipped tantalum bead. Nice caps, very low ESR and supposedly very reliable, claim "no-known wear-out mechanism". piglet Do you mean polymer aluminums? Those are great, super low ESR. We use United Chem-Com and Nichicon. 47 cents for 180 uF 6.3 volts, about 2x tha price of a regular aluminum cap. No, I don't think these are polymer, may even predate polymer electrolyte. Uses Mn02 I think like solid Ta. See Vishay SAL 122 series. Temp range -55 to +175 C. piglet |
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